Gas turbine engines, such as turbofan gas turbine engines, may be used to power various types of vehicles and systems, such as, for example, aircraft. Typically, these engines include turbine airfoils (or airfoils) that are impinged by high-energy compressed air that causes a turbine of the engine to rotate at a high speed. Consequently, the airfoils are subjected to high heat and stress loadings which, over time, may reduce their structural integrity.
Modern aircraft jet engines have employed internal cooling systems in the airfoils to maintain the airfoil temperatures within acceptable limits. Typically, the airfoils are air cooled using, for example, bleed air from a compressor section of the engine. The air may enter near the airfoil root, and then flow through a cooling circuit formed in the turbine airfoil. The cooling circuit typically consists of a series of connected cooling passages that form serpentine paths, which increase the cooling effectiveness by extending the length of the air flow path.
One exemplary cooling system is multi-walled and includes independent cooling circuits for the various surfaces of an airfoil, such as pressure and suction side surfaces, to thereby control specific heat load distributions thereon. The walls form intricate passages through which the cooling air flows to feed serpentine thin outer wall passages that incorporate pin fins, turbulators, turning vanes, and other structures therein. Although the cooling system operates adequately to cool most of the airfoil's pressure and suction side surfaces, it has been found that some portions of the airfoil may not be sufficiently cooled. Specifically, in some instances when these portions are exposed to extreme heat environments, they may oxidize, fatigue, and may become prematurely worn.
Hence, there is a need for an improved cooling system that is capable of cooling turbine airfoils in extreme heat environments without allowing the airfoil to fatigue or become prematurely worn. Additionally, it would be desirable for the system to be designed such that the airfoil may be manufactured relatively easily and inexpensively. Furthermore, other desirable features and characteristics of the present invention will become apparent from the subsequent detailed description and the appended claims, taken in conjunction with the accompanying drawings and this background of the invention.